1. Field of the Invention
The present invention relates to aqueous alkyldiketene dispersions which contain a C.sub.14 -C.sub.22 -alkyldiketene and from 1 to 10% by weight of a polymeric protective colloid and the use of the aqueous alkyldiketene dispersions as engine size in the production of paper, board and cardboard and for rendering cellulosic fibers water-repellent.
2. Description of the Background
Alkyldiketenes are used in the form of aqueous dispersions as size for paper. They are emulsified in water in the presence of emulsifiers or organic thickeners (cf. U.S. Pat. No. 2,627,477 and U.S. Pat. No. 3,130,118). The last-mentioned publication discloses the preparation of aqueous alkyldiketene dispersions with cationic starch. The low-concentration alkyldiketene dispersions described therein have a sufficiently long shelf life for use as size, but aqueous alkyldiketene dispersions having fatty alkyldiketene concentrations of more than 12% become solid relatively rapidly.
Various substances have already been used for stabilizing aqueous dispersions of fatty alkyldiketenes. For example, U.S. Pat. No. 2,901,371 and U.S. Pat. No. 3,311,532 disclose the use of higher fatty acids, their anhydrides, amides, aldehydes and acyl chlorides. The concentrations of fatty alkyldiketenes in the aqueous dispersions is, however, always below 10% by weight.
DE-A-2 514 128 discloses aqueous dispersions of ketene dimers which contain from 1 to 30% by weight, based on ketene dimers, of polyvinylpyrrolidone and/or polyvinylcaprolactam. They may furthermore contain an emulsifier, such as a fatty alcohol sulfate or a salt of a sulfonic acid which is obtained by sulfonation of an ethoxylated fatty alcohol or a cationic emulsifier which is prepared, for example, by reaction of oleylamine with ethylene oxide and quaternization with dimethyl sulfate. For the preparation of aqueous alkyldiketene dispersions having a particularly long shelf life, according to this publication an inert solvent, such as toluene or cyclohexane, is additionally used in dispersing the alkyldiketenes.
According to DE-A 3 316 179, from 4 to 12% strength aqueous alkyldiketene dispersions are obtained if alkyldiketenes are dispersed in water in the presence of cationic starch and a cationic protective colloid, the protective colloid being a water-soluble condensate which is obtainable by grafting polyamidoamines with ethyleneimine and crosslinking the polyamidoamines grafted with ethyleneimine with at least difunctional crosslinking agents. In order to increase the stability of the aqueous dispersion, water-soluble dicyandiamide/formaldehyde condensates must be added. According to the examples, the alkyldiketene concentration in the aqueous dispersions is 6% by weight.
EP-B-0 341 509 discloses a size mixture which contains, as essential components, an alkyldiketene and a hydrophilic polymer which is obtainable by polymerizing at least one hydrophilic vinyl monomer in the presence of from 0.01 to 10 mol % of an alkyl mercaptan having 6 to 22 carbon atoms in the molecule. According to Example 5, a copolymer of 97% of acrylamide and 3% of dimethylaminoethyl methacrylate is used as a hydrophilic vinyl polymer.
EP-B 0 437 764 discloses stable aqueous alkyldiketene dispersions which contain a protective colloid and an ester of a long-chain carboxylic acid and a long-chain alcohol in addition to an alkyldiketene. Preferred protective colloids are cationic starches. Sorbitan esters, soaps, synthetic detergents and thickeners, such as polymers of acrylamide, vinylpyrrolidone and N-vinyl-2-methylimidazoline, may also be used.
WO-A 94/12560 discloses condensates of polyalkylenepolyamines which are obtainable by
(a) partial amidation of polyalkylenepolyamines with monocarboxylic acids and PA1 (b) condensation of the partially amidated polyalkylenepolyamines with at least bifunctional crosslinking agents which have a halohydrin, glycidyl, aziridine or isocyanate unit or a halogen atom as a functional group PA1 (1) N-vinylpyrrolidone and PA1 (2) at least one quaternized N-vinylimidazole of the formula ##STR1## where R, R.sup.1 and R.sup.2 are each H, C.sub.1 -C.sub.4 -alkyl or phenyl, PA1 R.sup.3 is H, C.sub.1 -C.sub.18 -alkyl or benzyl and PA1 X.sup..crclbar. is an anion, PA1 (1) partial amidation of polyethyleneimines with monocarboxylic acids and PA1 (2) condensation of the partially amidated polyethyleneimines with at least bifunctional crosslinking agents which have a halohydrin, glycidyl, aziridine or isocyanate unit or a halogen atom as a functional group PA1 (1) the amidated polyalkylenepolyamines are reacted with PA1 (2) bifunctional or polyfunctional crosslinking agents in a weight ratio (a):(b) of from 1:0.001 to 1:10, preferably from 1:0.01 to 1:3. PA1 (1) partial amidation of polyethyleneimines having from 10 to 50,000 ethyleneimine units with monocarboxylic acids and PA1 (2) condensation of the partially amidated polyethyleneimines with epichlorohydrin, .alpha.,.omega.-bis(chlorohydrin)polyalkylene glycol ethers, .alpha.,.omega.-(glycidyl)ethers of polyalkylene glycols, .alpha.,.omega.-dichloropolyalkylene glycols, .alpha.,.omega.-dichloroalkanes or vicinal dichloroalkanes or mixtures thereof
to give crosslinked polyalkylenepolyamines which have a viscosity of at least 100 mPa.s in 20% strength by weight aqueous solution at 20.degree. C. The condensates are used as drainage aids, flocculants, retention aids and fixing agents in papermaking.
The stability of the aqueous diketene dispersions described above is still unsatisfactory.